Non-uniform polycrystalline composite and its method of manufacture

ABSTRACT

A polycrystalline diamond composite including a generally circular sintered polycrystalline cutting disc and a refractory substrate operationally connected to the polycrystalline cutting disc. The polycrystalline cutting disc further includes a plurality of coarse diamond grains and a plurality of fine diamond grains. The plurality fine diamond grains are concentrated in an annulus positioned to define an outer edge of the polycrystalline cutting disc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to co-pending U.S. patent application Ser. No. 14/248,717, filed on Apr. 9, 2014, which was a continuation of co-pending U.S. patent application Ser. No. 13/072,203, filed on Mar. 25, 2011, and also claims priority to co-pending U.S. provisional patent application Ser. No. 61/887,221, filed on Oct. 4, 2013.

TECHNICAL FIELD

The present novel technology relates to a polycrystalline diamond composite and a method to attach polycrystalline diamond cutting surfaces to substrates.

BACKGROUND

The conventional method to manufacture Polycrystalline Diamond Composite (PDC) is to start with diamond grains which are placed inside an enclosure. The enclosure usually used is made up of a refractory metals or materials, as shown in FIG. 1. The diamond grains are sintered together by the formation of carbon-to-carbon bonds between carbon atoms in adjacent diamond grains. In order to facilitate this binding process, a catalyst metal, typically cobalt, is used; however, metals selected from Group VIII of the periodic table, such as nickel, iron, cobalt and alloys thereof, have been used successfully as catalysts to facilitate the formation of carbon-to-carbon sp³ bonds between diamond grains within the PDC body during sintering. During the sintering process, diamond grains are subjected to a pressure of around 55 Kbar or higher along with a temperature around 1500° C. In this temperature-pressure regime, and especially in the presence of a catalyzing metal, sp³ type bonds between carbon atoms in adjacent diamond grains are formed rendering the collection of diamond grains into a solid body known as a polycrystalline diamond composite or PDC.

To facilitate the use of this solid PDC in wear resistant and/or impact resistant applications, it is typical to attach a solid PDC layer to a solid tungsten carbide matrix or like support substrate. The tungsten carbide substrate typically contains cobalt metal as a binder matrix. Attachment of PDC to the tungsten carbide substrate is usually done under high pressure and high temperature (HPHT), more typically during the sintering process. Under the high pressures and high temperatures achieved during the sintering process, cobalt metal within the substrate melts and infiltrates the interstices between diamond grains acting as the catalyst during sintering. The end product is a two layered structure, as shown in FIG. 1, with the majority of the top part of the structure being composed of sintered diamond (the sintered diamond body is typically composed of 90% or higher of diamond by volume); the diamond is infiltrated with cobalt and/or tungsten and/or alloys of cobalt and tungsten and carbon.

Another method of making PDCs is to start with a sintered diamond layer of PDC and then attach the sintered PDC to a substrate. The solid PDC layer typically contains cobalt and/or cobalt tungsten alloys within the interstitial spaces located between diamond grains. These interstitial spaces are generally interconnected to define open pore structures. Prior to attaching the solid PDC to a solid tungsten carbide or like substrate, the cobalt and/or cobalt-tungsten alloys within the interstitial spaces within the solid PDC are removed by introducing the PDC to an acid to leach out the metals from the solid PDC. Leaching the catalyst metal involves exposing the PDC to a typically heated strong acid or a combination of acids, such as nitric acid, hydrofluoric acid, hydrochloric acid, perchloric acid, and combinations thereof.

Once the catalyst metal is removed from the PDC layer, the remaining sintered PCD layer is often referred to as a Thermally Stable Polycrystalline diamond or TSP. Attaching the TSP to a substrate is typically done under HPHT conditions. The TSP and substrate are placed in contact with each other and are subjected to the HPHT conditions, similar to the sintering conditions. Once the substrate is sufficiently heated, the metal binder within the substrate melts and penetrates the TSP. Upon cooling, the liquid metal solidifies and acts as a glue attaching TSP to substrate (FIG. 2). However, preparing the TSP as described above presents many challenges. Principal among these is coaxing molten cobalt and/or cobalt tungsten alloy to fully penetrate the open porosity of the TSP to fill the interstitial spaces. Such penetration is necessary in order to allow pressure transmission within the body of the TSP. The TSP volume is composed of diamond grains bound together by SP³ type bonds and interstitial spaces that have been cleared of catalyst metal.

In order to protect the diamond grains during the HPHT carbide substrate/TSP attachment process, the diamond grains are typically maintained under elevated pressure at the elevated HPHT temperatures, which may reach 1500 C. The diamond grains are typically maintained within the temperature-pressure regime of the carbon phase diagram in which diamond is the stable form of carbon. The TSP surfaces are exposed to elevated pressure in HPHT to keep the diamond grains in the diamond stable pressure-temperature region. However, the grains within the body of the TSP may still be exposed to lower pressure and without a medium to transmit pressure into the interstitial spaces within the TSP body, diamond grains within the TSP body will convert to graphite since the prevailing pressure within the TSP is less than that required to maintain the diamond within the diamond stable region.

The molten cobalt and cobalt alloys that penetrate within the interstitial spaces within the TSP body act as a pressure transmission medium, since liquids act as isobaric pressure transmitters. Therefore during HPHT the molten cobalt and cobalt alloys penetrate the TSP body and fill the void interstitial spaces to protect diamond grains by maintaining sufficient pressure to keep them from converting to graphite.

The size of the interstitials spaces is determined by the diamond grain size and diamond grains shape. The larger diamond grains result in larger interstitial spaces. Also, smaller grain sizes result in a larger overall surface area within the TSP that the molten cobalt and/or cobalt alloy will need to wet in order to fill the interstitial spaces, more surface area the molten metal has to flow over presents more friction resistance to the molten metal flow. When comparing a TSP composed of larger diamond grains to one composed on smaller grain size, the pore structure of the TSP composed of larger diamond grains is likewise larger. Thus, it is more difficult to fill the interstitial spaces within the TSP composed of smaller grains since these spaces tend to be narrower and harder to fill with liquid metal, in part due to the surface tension of the liquid metal. This results in lower yield and more defects when attaching TSP's of smaller grains compared to more desirable yield and defect rates of TSP composed of larger grains.

The smaller the diamond grains used to make the TSP the more difficult it is to attach the TSP to a carbide substrate in HPHT. However, TSP's composed of smaller grains are desired in applications that require abrasion resistance. A TSP composed of small diamond grains has a larger density of diamond-to-diamond SP³ bonds. Thus, PDC's characterized by finer grain sizes tend to be harder, but are more difficult to make due to the smaller interstitial spaces that need to be filled with liquid metal and, consequently, present higher resistance to metal infiltration due to the increased interior surface area of the pore structure that the metal has to wet while filling the smaller spaces. Thus, there is a need of a TSP body having the abrasion resistance associated with fine diamond grain size but with the substrate attachment ability associated with a coarser diamond grain size. The present novel technology addresses this need.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a conventional prior art PDC.

FIG. 2 is an illustration of a two-layered sintered prior art PDC.

FIG. 3A is a first plan view illustration of a first embodiment of the novel technology PDC.

FIG. 3B is a side elevation view of FIG. 3A.

FIG. 4A is an exploded side elevation illustration of one embodiment of the novel method for manufacturing the novel PDC.

FIG. 4B is an exploded perspective view of FIG. 4A.

FIG. 5A is a top plan illustration of the regions of a polycrystalline layer.

FIG. 5B is a side elevation cutaway view of FIG. 5A.

FIG. 5C is a partial exploded view of the outer ring of FIG. 5B.

FIG. 5D is a partial exploded view of the inner ring of FIG. 5B.

FIG. 6A is a partial top plan view of a polycrystalline layer according to one embodiment of the present novel technology.

FIG. 6B is a cross-sectional view of FIG. 6A.

FIG. 6C is a partial top plan view of a polycrystalline layer according to another embodiment of the present novel technology.

FIG. 6D is a cross-sectional view of FIG. 6B.

FIG. 6E is a partial exploded view of FIG. 6D.

FIG. 7 is a carbon phase diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the claimed technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the claimed technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the claimed technology as illustrated therein being contemplated as would typically occur to one skilled in the art to which the claimed technology relates.

The novel polycrystalline diamond layer structure may vary for several reasons. In some embodiments, the structure is a single layer of diamond where the properties of the diamond grains within this layer are homogeneous or similar throughout the layer. In other embodiments, the PDC layer may be made of multiple sub-layers stacked on top of each other, each sub-layer having properties different from adjacent layers, wherein the change in properties from layer to layer may be gradual or may be abrupt, as desired. Different sub-layers within the PDC layer may also contain constituents other than diamond. Commonly used constituents are tungsten carbide grains, other metal carbides, compounds, and/or elements used to provide the PDC layer with desired physical and/or chemical properties.

One embodiment of the present novel technology is the PDC layer 10 shown in FIG. 3. In this embodiment, the PDC layer 10 is formed having an annulus portion 15 of fine diamond grains 20 surrounding the remainder or core portion 25 of the PDC layer 10, which is formed from coarse diamond grains 30. The finer diamond particles 20 are typically between the sizes of 1 to 30 micron in diameter, although larger particle sizes may be elected as long as the diamond particle size in the core portion 25 and the rest of the PDC body 10 is relatively coarser. The coarser diamond particles 30 are typically between the sizes of 12 to 100 micron in diameter, but may likewise fall outside this range, as long as the relatively coarser diamond particles 30 in one region are larger than the relatively finer diamond grains 20 in the annulus region 15. Particle size typically refers to average or mean sizes. Typically, the closer the mean sizes are, the easier it is to make a defect-free PDC body. The farther apart the mean sizes are, the more attention will have to be paid to compaction and fill quality or density distribution of the grains 20, 30. When the size ratio is more than 1½ times between coarse grains 30 and fine grains 20, the sintering quality of the fine diamond grains 20 may be adversely affected, all other factors being equal.

In this embodiment, it is easier to sweep and sinter the PDC layer 10, which produces a PDC with a high density of spa type bonds. Sintered bodies with a fine grain diamond microstructure may offer improved abrasion resistance over those having a coarser grain diamond microstructure. Since the outer edge 35 of the polycrystalline diamond layer 10 does most of the cutting and experiences most of the abrasion wear, the outer edge 35 is typically formed from fine grained diamond precursors 20 oriented as an outer annulus 15. Since coarse grain diamond microstructures may offer better impact resistance over fine grain diamond microstructures, a PDC layer 10 having coarser grains 30 in the majority of its volume may provide the PDC composite body 40 with improved impact resistance.

The annulus 15 portion is typically not as thick as the PDC disc 10. In other words, the PCD disc 10 typically has a thickness defined as the distance between the top disc face and the bottom, parallel disc face. The annulus 15 typically extends from the top disc face towards the bottom disc face, but typically does not reach the bottom disc face.

In some embodiments, a PDC layer 10 may need to be attached or re-attached to a substrate 45. In one embodiment, a pre-sintered, metal-free PDC layer 50, or TSP, may be attached or re-attached to a tungsten carbide substrate 45. The pre-sintered metal-free PDC layer 50 may be placed into a refractory metal cup 55 and the carbide substrate 45 may be placed in contact with one side of the PDC layer 50 to define a bilayer 60, as illustrated in FIG. 4. The sintered polycrystalline diamond layer-substrate combination 60 may be subjected to temperatures of approximately 1500° C. and pressures of approximately 55 Kbar, the pressure applied in the re-attachment may be similar to the original pressure and heat conditions used to make a conventional PDC. Typical pressure range to sinter PDC is 55 to 85 Kbar, however, pressures of 125 Kbar in laboratory environments have been used successfully to sinter diamond, temperatures needed to sinter diamond are the temperatures required to melt the metal catalyst and maintain carbon in the diamond stable region. Cobalt catalyst is typically used and has a melting temperature of 1495° C., although lower melting cobalt alloys of around with melting points around 1200° C. may be used. Temperatures of 1800° C. with higher corresponding pressures from the in the diamond stable region may be used to sinter diamond. Similar HPHT conditions that are used for diamond sintering may be used to re-attach the TSP However, any pressure and temperature sufficient to partially or completely melt the substrate 45 to facilitate penetration of the polycrystalline diamond layer 50 may be used. At elevated temperatures cobalt metal, cobalt-tungsten carbon alloy, or the like used to bind the tungsten carbide substrate 45 may melt. The high pressure environment surrounding the assembly 60, while increasing the melting point of the cobalt, can force the molten cobalt 65, molten cobalt alloy 65, or the like to penetrate through the TSP 50. The penetrating molten metal 65 catalyst binds the tungsten carbide substrate 45 to the pre-sintered PDC 50.

According to one method of manufacturing a PDC 10 having an annulus 15 of fine diamond grains 20 surrounding the core portion 25 of the PDC layer 10 as is formed from coarse diamond grains 30, a TSP 50 is produced as shown in FIGS. 4 & 5 by first acid leaching metal from the pre-sintered PDC 50. Such a TSP 50 is typically easier to attach to a carbide or like substrate 45 than a TSP 50 that is made from one layer composed solely of fine diamond grains 20, or diamond grains all falling into a relatively narrow PSD. Typically, at least about 50% by volume of such a TSP 50 is composed of coarse grains 30 which give rise to larger intergranular pores 70 presenting less resistance to being filled with molten cobalt and cobalt tungsten alloys 65. This improves the yield and reduces defects of the product.

In an alternate embodiment, the starting material may be metal free, pre-sintered PDC 50. However, various PDC layer designs may be used, such as single layer, multiple layer, and, the like. In this embodiment, a PDC layer 50 composed of two regions, as shown in FIG. 5, may be used to make the re-attached PDC. The PDC layer may be include an annulus 15 of fine grain diamond encircling a core portion 25 made of coarse grained diamond 30. FIG. 6 shows a variation of the aforementioned PDC structure, in addition to an annulus 15 of fine grain diamond 20, another fine grained region may be formed by one, and more typically two, channels or bands 80. The two channels 80 are typically oriented perpendicular to each other, and more typically cross the each other at the center of the PDC layer 50. In other words, the channels 80 are typically perpendicular to each other and both channels 80 bisect the PDC disc 50, with a first band 80 extending from a first point on the outer edge 35 of the polycrystalline cutting disc 10 to a second, spaced point on the outer edge 35 of the polycrystalline cutting disc, and a second band 80 extending from a third, spaced point on the outer edge 35 of the polycrystalline cutting disc 10 to a fourth, spaced point on the outer edge 35 of the polycrystalline cutting disc 10.

The addition of the intersecting channels 80 may reduce the residual stress within the PDC layer 50. The novel technology allows for the coarse diamond grains 30 to present less resistance to catalyst penetration into the metal free PDC layer 50. The coarse grains 30 are more resistant to being crushed when subjected to high sintering pressure during the re-attachment process. Thus, fine grains 20 may present a challenge in re-attachment process. In one embodiment, the PDC layer 10 offers the more attractive properties of a fine diamond grain microstructure on the cutting edge 35 while employing coarser-grained microstructure regions to reduce the chance of crushing the diamond grains.

In some embodiments, before re-attachment may occur metal-free PDC 50 may be prepared. PDC layers 10 may be soaked in acid while heat is applied, with or without applied pressure, to leach metal from the PDC layer 50.

In some embodiments, during the PDC reattachment process heat may not be evenly distributed throughout the PDC layer. For example, the PDC portion close to the outside diameter is typically hotter than the rest of the PDC. With the proposed PDC layer design in this novel technology, the higher temperature refractory metal close to the PDC layer 50 may aid penetration through the fine grained diamond regions 15, 80.

In operation, a polycrystalline diamond portion 10, 50 may be attached to substrate 45 by first positioning at least one polycrystalline diamond layer 10 in mechanical communication with a substrate 45 to define a bilayer 60. Then, the bilayer 60 is heated to a temperature sufficient to at least partially melt the substrate 45 to yield molten substrate material 65, and sufficient pressure is applied to the bilayer 60 to urge penetration of molten substrate material 65 into the polycrystalline diamond layer 10, 50. The polycrystalline diamond layer 10, 50 is bonded to the substrate 45 as the molten metal 60 cools and solidifies. Typically, the substrate 45 is tungsten carbide. More typically, the bilayer 60 is heated to about 1500° C. under a pressure of about 55 Kbar, which may be applied sequentially or simultaneously. Typically, the molten substrate material 65 contains cobalt. The substrate 45 may be monolayered or multilayered, and the PDC layer 10, 50 may be a non-uniform mixture of a coarse diamond grains 30 and fine diamond grains 20.

While the claimed technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the claimed technology are desired to be protected. 

What is claimed is:
 1. A polycrystalline diamond composite comprising: a generally circular sintered polycrystalline cutting disc; and a refractory substrate operationally connected to the polycrystalline cutting disc; wherein the polycrystalline cutting disc further comprises: a plurality of coarse diamond grains; and a plurality of fine diamond grains; and wherein the plurality fine diamond grains are concentrated in an annulus positioned to define an outer edge of the polycrystalline cutting disc.
 2. The polycrystalline diamond composite of claim 1, wherein the polycrystalline cutting disc has a first circular flat surface and a second, oppositely disposed flat circular surface spaced from and oriented parallel to the first circular flat surface; wherein the distance between the first and second circular flat surfaces defines a disc thickness; and wherein the annulus extends from the first surface toward the second surface.
 3. The polycrystalline diamond composite of claim 2, wherein the annulus is thinner than the disc thickness.
 4. The polycrystalline diamond composite of claim 2, wherein the a plurality of fine diamond grains are concentrated in the annulus positioned on the first circular flat surface and to positioned to define the outer edge of the polycrystalline cutting disc, in a first band extending from a first point on the outer edge of the polycrystalline cutting disc to a second, spaced point on the outer edge of the polycrystalline cutting disc, and in a second band extending from a third, spaced point on the outer edge of the polycrystalline cutting disc to a fourth, spaced point on the outer edge of the polycrystalline cutting disc.
 5. The polycrystalline diamond composite of claim 4 wherein the first and second bands are oriented perpendicularly to one another; and wherein the first and second bands bisect the first circular flat surface.
 6. The polycrystalline diamond composite of claim 4 wherein the first and second bands are thinner than the disc thickness.
 7. A method for attaching a polycrystalline diamond portion to a substrate comprising: a) positioning at least one polycrystalline diamond layer in mechanical communication with a substrate to define a bilayer; b) heating the bilayer to a temperature sufficient to at least partially melt the substrate to yield molten substrate material; c) applying sufficient pressure to the bilayer to urge penetration of molten substrate material into the polycrystalline diamond layer; and d) bonding the polycrystalline diamond layer to the substrate.
 8. The method of claim 7 wherein the substrate is tungsten carbide.
 9. The method of claim 7 wherein during b), the bilayer is heated to about 1500° C.
 10. The method of claim 7 wherein during c) the bilayer is under about 55 Kbar.
 11. The method of claim 7 wherein the molten substrate material contains cobalt.
 12. The method of claim 7 wherein the substrate is multilayered.
 13. The method of claim 7 wherein the polycrystalline layer further comprises a non-uniform mixture of a coarse diamond grains and fine diamond grains.
 14. The method of claim 13, wherein a plurality of fine diamond grains defines an outer annulus around an outer the polycrystalline diamond layer.
 15. The method of claim 7 wherein the polycrystalline diamond layer is pre-sintered.
 16. The method of claim 7 wherein before c), the polycrystalline diamond layer is substantially metal-free.
 17. The method of claim 7 wherein steps a) and b) occur substantially simultaneously. 